The beaches in Vallarta are nice in either the south side around the Dreams area or the north side in the Punta de Mita, Nuevo Vallarta (Dreams Villamagna) and Bucerias area. If you want to have more variety do what most brides are doing now which is to have your guests stay in an AI and have the actual reception in a private venue. For example a garden on the beah or villa. This gets the guests out of the hotel for a day and let's them see the other areas.
Beach wise I think the Dreams in NUevo has the better beach than the Dreams in the south (original one). Also resort wise the Dreams in the south is run down compared to the north side one Villamagna. If you like nicer places go Villamagna, if you like jungle and somewhat more rustic rooms and old instalations go with Dreams south. If you have to go with Dreams.
Good luck, either place will be fun. The beaches are both nice and safe. Nuevo Vallarta has miles of beach compared to the beach in the south one that has maybe 700 yards wide... I just remembered that... if you like walking on the beach or you have excersize joggers go with Nuevo for sure....
Sorry, I hope that helps. We are in Bucerias which is 15 minutes north of the Villamagna Dreams. Even we go to the south side sometimes to get a different beach... so both beaches are great in their own way. I would let the resort itself be the tie breaker!
Bucerias beach which connects 6 miles up the beach with Dreams Villamagna in NUevo Vallarta which are the buildings you see far away from the pool under the clouds... hope this helps!